Interdigitated electrode structures for both chemical and non-chemical sensing and transducer applications have been around and described in literature for a long time. They typically include a large number of long and narrow conductors (referred to as “fingers”), arranged in a single plane parallel to one another, and grouped and electrically connected into two- or multiple port electrical elements.
Various nomenclature is used in the technical and scientific literature to identify these types of sensing electrode structures, e.g., IDE (Interdigitated Electrode), FEF (Fringing Electric Field Sensors), Interdigital Sensors and Transducers, and the like. These sensing electrode structures are often implemented as co-planar, patterned metal layers on a substrate, fabricated using thin-film and/or semiconductor type processes. When used as sensors, interdigitated electrodes typically interrogate an area of space between and/or above the metal layers, and detect small changes in the electrical properties of any material or substance occupying that space. A particular concern with such sensors is that the sensors respond only to the electrical properties of the sensor material, and not to the electrical properties of the fluid beyond this sensor material. When a sensor exhibits such an undesired response to the electrical properties of the fluid beyond the sensor material, instead of just to the electrical properties of the sensor material itself, this problem is denoted by terms such as “read-through,” commonly used in association with insulating fluids, or the “third electrode effect,” commonly used in association with conductive fluids.